Depends on if the vehicles are used solely for business use, (kind of) if they are then just use the whole of the petrol receipt as an expense on the business, less any cheeky purchases of the odd kitkat (other brands of chaoclate are also available see your local petrol station for more details)
If its a Private car you use fgor business then apportion the cost, is it use 75% business, 80%? then deduct the personal usage off the petrol reciept. :D
ahh, so what if we put £50 of petrol in a month each but pay with our business account debit card but only 50% of that is business, how would i record that in the books?